Waveguide hybrid junctions with perpendicularly disposed, overlapping waveguide sections forming cruciform matching section



1965 B. M. SCHIFFMAN $234,712

WAVEGUIDE HYBRID JUNCTIONS WITH PERPENDICULARLY DISPOSED, OVERLAPPING WAVEGUIDE SECTIONS FORMING CRUGIFORM MATCHING SECTION Filed Sept. 13) 1962 m, A 5' INVENTOR.

BERNARD M. SCHIFFMAN BY WW ATTORNEY United States Patent O WAVEGUIDE HYBRID JUNCTIONS WITH PERPEN- DICULARLY DISPOSED, OVERLAPPING WAVE- GUIDE SECTIONS FORMING CRUCIFORM MATCHING SECTION Bernard M. Schiifman, Palo Alto, Calif., assignor to Varian Associates, Palo Alto, Calif., a corporation of California Filed Sept. 13, 1962, Ser. No. 223,507 9 Claims. (Cl. 3337) The present invention relates in general to Waveguide hybrid junctions, and more particularly to novel waveguide hybrid junction structures presenting an improved impedance match when utilizing coaxial line balanced connections.

In US. Patent 3,066,290, assigned to the present assignee, there is disclosed and claimed a class of extremely compact and lightweight balanced hybrid junctions comprising a section of hollow waveguide (usually, rectangular or circular) capable of sup-porting two axially propagating orthogonal Waveguide modes established by the waves propagated through two of the junction connections, said Waveguide section being provided with a structure which perturbs said modes so that the two modes are in-phase in the third junction connection and out-of-phase in the fourth junction connection thereby providing a broadband balanced coupling to said third and fourth connections.

It has been found that undesirable impedance mismatches are encountered when coaxial line structures are used for the balanced (third and fourth) connections. Thus, in the case of a microwave mixer the balanced connections usually consist of dielectric cartridge-type diode rectifiers (for example, type IN 415) inserted directly into the waveguide, these rectifiers being fairly well matched to the waveguide impedance of several hundred ohms. Such rectifiers, however, are not readily available for all conditions of operation. For example, at frequencies on the order of 13.3 to 13.7 kmc./s (Ku band) which are of special interest in airborne navigation, the most satisfactory rectifiers now available are of a type wherein the rectifying junction is mounted within, and matched to, a coaxial line structure having an impedance on the order of only 65 ohms.

Thus, a principal object of the present invention is the provision of novel waveguide hybrid junction structures which operate eiliciently with coaxial line balanced connections.

One feature of the present invention is the provision of an orthogonal mode waveguide junction with a cruciformshaped cross-section.

Another feature of the present invention is the provision of an orthogonal mode waveguide junction having axiallyaligned and orthogonally disposed ridged waveguides.

Still another feature of the present invention is the provision of an orthogonal mode waveguide junction having a metallic block therein for presenting a capacitive shunt susceptance to one connecting waveguide and for enabling capacitive coupling to a ridge in the other connecting Waveguide.

These and other features and advantages of the present invention will be more apparent after a perusal of the following specification taken in connection with the accompanying drawings wherein,

FIG. 1 is a schematic perspective view of a prior art orthogonal mode waveguide junction,

FIG. 2 is a schematic perspective view of an orthogonal mode waveguide junction in accordance with the present invention,

FIG. 3 is a cross-sectional view taken along line 3-3 in FIG. 2,

FIG. 4 is a front perspective view, in constructional 3,214,712 Patented Oct. 26, 1965 ice detail, of a balanced microwave mixer in accordance with the present invention,

FIG. 5 is a rear perspective view of the mixer of FIG. 4,

FIG. 6 is a cross-sectional view taken along line 6-6 in FIG. 4,

FIG. 7 is a cross-sectional view taken along line 7-7 in FIG. 4.,

FIG. 8 is a cross-sectional view taken along line 8--8 in FIG. 7, and

FIG. 9 is a cross-sectional view taken along line 99 in FIG. 7.

FIG. 1 schematically illustrates a prior art orthogonal mode microwave mixer wherein a substantially square waveguide section 1 is energized in two orthogonal modes by a vertically polarized signal wave propagated through a horizontally disposed rectangular waveguide 2 at the left Wall thereof, and by a horizontally polarized local oscillator wave propagated through a vertically disposed rectangular Waveguide section 3 at the right wall thereof, one mode corresponding to each input wave. Positioned inside the waveguide section 1 is a pair of crystal diode rectifiers 4 and 5 contacted at the oppositely-poled inwardly extending terminals thereof by a horizontal output post 6. The electric field of the signal wave is unperturbed by the post 6 and couples into each of the crystal rectifiers 4 and 5 in the same direction as indicated by the dot-dash arrows. The local oscillator wave, however, is perturbed by the post 6 in such a manner that the electric field thereof couples ito each crystal rectifier in an opposite direction as indicated by the dotted arrows. The difference between the currents in the separate rectifiers flows along the conductor 6 through a low-pass insulating choke 6' in the rear waveguide wall to the inner coaxial conductor of a balanced I.F. beat frequency output, the current components in the separate crystal rectifiers due to local oscillator noise canceling each other at the junction of post 6.

As previously described, an undesirable impedance mismatch occurs when coaxial line type rectifiers are used in this simple junction arrangement. According to the present invention, this is overcome by the arrangement schematically illustrated in FIGS. 2 and 3 wherein the orthogonally disposed connecting waveguides 2 and 3 overlap slightly to form a junction region 1 of cruciform-shaped cross-section. The inner conductors of coaxial line structures 4', 5 (inside of which the rectifying crystals 4, 5 are disposed) extend into the junction region 1 and contact the LP. output post 6, such that the waveguide fields excite currents which are conducted to the crystals 4, 5 and the beat frequency current resulting from the mixing action of crystals are conducted to the post 6 in a balanced manner. It will be noted that the cruciform-shaped junction 1 permits the establishment of orthogonal modes with an advantageous lowering of the waveguide impedance for improving the impedance match to the coaxial lines 4 and 5.

Additional impedance-matching structure will be described by reference to FIGS. 3-6 which show the construction of an exemplary mixer in accordance with the present invention. Embodiments of this example have been made to operate over the frequency range of 13.3 to 13.7 kmc./s. with a maximum noise figure of 10 db at 13.5 kmc./s. including 30 mc./s. I.F. strip and image frequency contributions. The signal and local oscillator input VSWR is less than two to one over a 500 mc./s. bandwidth. The entire structure measures only 1% x 1 x inches and weighs less than two ounces.

The main structural element of this embodiment is a solid metallic block 1' in which the overlapping waveguides 2 and 3 are formed by recesses through the front and rear surfaces, respectively, using the orientation of FIG. 4 as a reference. Suitable threaded holes are provided through the front surface for mating to a vertically polarizing signal Waveguide extension, and similar holes .11 are provided through the rear surface for mating to a horizontally polarizing local oscillator waveguide extension. The crystal-supporting coaxial line structures 4' and 5, for example type IN 78 crystal rectifiers, are seated in cap assemblies 12 removably inserted through the top and bottom surfaces, and the inwardly extending inner conductors thereof are secured in contacting relation by opposed recesses in junction block 13. The output I.F. post 6 is attached to the block 13, and extends through the insulating low-pass choke 6 in the back wall of waveguide junction region 1, in a direction mutually perpendicular to the waveguide and coaxial line axes, to form the inner conductor of the output coaxial I.F. connector 6".

Details of the crystal cap assembly 12 are seen in FIG. 6. Only the top assembly is shown, since the bottom assembly is identical thereto. The outer conductor of the coaxial line structure 4' is seated in threaded bushing 14 having a radial flange insulatedly joined via cement 15 to concentric bushing 16, this latter bushing being held in contacting relation to the grounded junction block 1' by set screw 17. The outer conductor of the coaxial line structure 4' also bears against a bore 18 formed through the top surface of junction region 1, and is insulated therefrom by an insulating coating on the bore 18 which forms a high capacitance microwave bypass. A small resistor 19 returns the crystal current to the ground, thereby applying a DC. voltage to lug assembly 20 (threaded on the bushing 14) to enable external monitoring of the DC. crystal current. A capacitor 21 provides a by-pass to ground for AC. crystal current components in order to reduce undesirable leakage fields at the monitoring lug 20.

The additional impedance matching structure includes a double ridge 22 for the signal waveguide 2 and a single ridge 23 for the local oscillator waveguide 3, these ridges providing impedance transformation from the connecting waveguides to the lower impedance junction region 1. The junction block 13 is enlarged to extend into the signal waveguide 2 in order to present a capacitive shunt susceptance which tunes out the inductive reactance presented to the signal Wave by the T-branching of the coaxial lines 4, 5'. The local oscillator waveguide ridge 23 has a finger 23' (FIG. 7) extending into the junction to provide a capacitance coupling to the opposite fiattened surface of the junction block 13. Fine tuning adjustments are effected by a screw 24 extending into the local oscillator Waveguide 3 opposite ridge 23, and by a screw 25 extending into the junction 1 in axial alignment with the LR post 6.

Certain possible modifications of the present invention should be particularly noted. Since the junctions of the present invention are reciprocal hybrid devices, the roles of the various terminals can, under suitable conditions, be reversed. For example, in the case of a mixer the signal and local oscillator inputs could be reversed; or the mixer operated as a side-band modulator by using the LP. post as the input terminal for the modulating signal and the opposite waveguide connections for the carrier input and modulated output, respectively. Further, the mixer may be operated as a parametric amplifier by using voltage-controlled diode capacitors instead of dissipative diode rectifiers. Still further, it may be desirable in some instances to establish a waveguide mode of desired polarization by means of a junction connection consisting of a coaxial probe rather than a single mode waveguide.

Since many changes can be made in the above construction and many apparently widely different embodiments of this invention could be made without departing from the scope thereof, it is intended that all matter contained in the above construction or shown in the accompanying drawing shall be interpreted as illustrative and not in a limiting sense.

What is claimed is:

1. A waveguide hybrid junction comprising: a pair of axially aligned and perpendicularly disposed rectangular waveguide sections adapted to propagate mutually orthogonally polarized Waves, said waveguide sections overlapping to form an orthogonal mode waveguide region of cruciform-shaped cross-section, said Waveguide sections having longitudinal axes that are parallel; and a pair of coaxial line connections communicating with said orthogonal mode waveguide region and adapted for balanced excitation by said waves.

2. A waveguide hybrid junction according to claim 1 wherein the inner conductors of said coaxial line connections are collinearly disposed in the polarization direc- V tion of one of said waves, and including means for perturbing the other of said waves so that it excites one of said connections in-phase with the excitation of said one wave, and excites the other of said connections out-ofphase with the excitation of said one wave.

3. A waveguide hybrid junction comprising: a hollow Waveguide section capable of supporting a pair of axially propagating orthogonally polarized waveguide modes, said waveguide section having a cruciform-shaped crosssection; at least one single mode waveguide section axially aligned with said orthogonal mode waveguide section and being ridged in order to provide an impedance match between said sections, said waveguide sections having longitudinal axes that are parallel; and a pair of balanced coaxial line connections communicating with said orthogonal mode waveguide section.

4. A microwave mixer comprising: a metallic block having axially aligned and perpendicularly disposed wave guide sections recessed through opposite surfaces thereof, said waveguide sections adapted to propagate mutually orthogonally polarized waves and overlapping to form a junction region of cruciform-shaped cross-section, said Waveguide sections having longitudinal axes that are parallel; and a pair of coaxial line type diode connections communicating with said junction region and adapted for balanced excitation by said waves.

5. A microwave mixer comprising: a metallic block having axially aligned and perpendicularly disposed waveguide sections recessed through opposite surfaces thereof, said waveguide sections adapted to propagate mutually orthogonally polarized waves and overlapping to form a junction region of cruciform-shaped cross-section, said waveguide sections having longitudinal axes that are parallel; and a pair of coaxial line type diode connections communicating with said junction region and adapted for balanced excitation by said waves wherein said diode connections have inwardly extending, oppositely poled, inner conductors collinearly disposed in the polarization direction of one of said waves, and including a conducting post contacting said inner conductors and insulatedly extending through said metallic block in a direction mutually perpendicular to the axis of said waveguide sections and the axis of said diode connections to provide a balanced beat frequency terminal.

6. A microwave mixer comprising: a metallic block having axially aligned and perpendicularly disposed waveguide sections recessed through opposite surfaces thereof, said waveguide sections adapted to propagate mutually orthogonally polarized waves and overlapping to form a junction region of cruciform-shaped cross-section, said waveguide sections having longitudinal axes that are parallel; and a pair of coaxial line type diode connections communicating with said junction region and adapted for balanced excitation by said waves wherein each of said waveguide sections is ridged in order to provide an impedance match to said junction region.

7. A microwave mixer according to claim 5 wherein said post contacts said inner conductors at a metallic junction block.

8. A microwave mixer according to claim 7 wherein said junction block has an enlarged section extending into that waveguide section having a wave polarization in the direction of said diode connections in order to present a capacitive shunt susceptance thereto. 5

9. A microwave mixer according to claim 8 wherein that waveguide section having a wave polarization in the direction perpendicular to the direction of said diode connections has a ridge with a finger portion extending into said junction region in capacitive coupling relation with 1 said junction block.

References Cited by the Examiner UNITED STATES PATENTS Rodwin 33311 Hanson et al. 33311 Stracca 333-11 Schiifman 325-446 Heningcr et a1 325-445 McEuen et a1 333--21 0 HERMAN KARL SAALBACH, Primary Examiner. 

1. A WAVEGUIDE HYBRID JUNCTION COMPRISING: A PAIR OF AXIALLY ALIGNED AND PERPENDICULARLY DISPOSED RECTANGULAR WAVEGUIDE SECTIONS ADAPTED TO PROPAGATE MUTUALLY ORTHOGONALLY POLARIZED WAVES, SAID WAVEGUIDE SECTIONS OVERLAPPING TO FORM AN ORTHOGONAL MODE WAVEGUIDE REGION OF CRUCIFORM-SHAPED CROSS-SECTION, SAID WAVEGUIDE SECTIONS HAVING LONGITUDINAL AXES THAT ARE PARALLEL; AND A PAIR OF COAXIAL LINE CONNECTIONS COMMUNICATING WITH SAID ORTHOGONAL MODE WAVEGUIDE REGION AND ADAPTED FOR BALANCED EXCITATION BY SAID WAVES. 